2,5-Furandicarboxylic acid, also known as dehydromucic acid is a furan derivative. This organic compound was first obtained by Fittig and Heinzelmann in 1876. The first review, by Henry Hill was published in 1901 (Am. Chem. Journ. 25, 439). FDCA was more than 125 years later identified by the US Department of Energy as one of 12 priority chemicals for establishing the “green” chemistry industry of the future. However, to date, no commercial process exists for its production. On laboratory scale it is often synthesized from 5-hydroxymethylfurfural (HMF), which in turn can be obtained from carbohydrate containing sources such as glucose, fructose, sucrose and starch. From fructose and glucose HMF is obtained by acidic elimination of three moles of water.
The derivatives of HMF are identified as potential and versatile fuel components and precursors for the production of plastics. The polyester from FDCA dimethyl diester and ethylene glycol was first reported in 1946 (GB 621,971).
WO 01/72732 describes the oxidation of HMF to FDCA. The maximum FDCA yield reported is 59%, obtained at 105° C. The oxidation of HMF in an aqueous medium with oxygen using a catalyst from the Pt-group is described in U.S. Pat. No. 4,977,283. Taarning et al. described the oxidation of HMF over gold based catalysts (ChemSusChem, 2008, 1, 1-4).
Partenheimer et al (Adv. Synth. Catal. 2001, 343, pp 102-11) describe the synthesis of 2,5-furandicarboxylic acid by catalytic air-oxidation of 5-hydroxymethylfurfural with metal/bromide catalysts such as Co/Mn/Br in acetic acid at temperatures ranging from 50 to 125° C. With the Co/Mn/Br catalyst the highest FDCA yield obtained is 35.2% (Table 3, experiment 4). On page 103 of the same paper, under the header “products formed” it is stated: “A side reaction is the esterification of the alcohols to form the more oxidatively stable acetate . . . ” As apparently 5-hydroxymethylfurfural reacts with acetic acid a loss of the starting material takes place. Further, in the reaction scheme given in FIG. 1 on page 103, it is indicated that 5-(acetoxymethyl)furfural is an end-point. There is no further reaction of this compound indicated to FDCA (in contrast to the ester of the intermediate product 5-(acetoxymethyl)furan-2-carboxylic acid). In other words, the 5-(acetoxymethyl)furfural (AMF) formed through reaction of HMF with acetic acid solvent, is not oxidized to FDCA and its formation leads therefore to yield loss.
This result was confirmed in U.S. 2009/0156841. Although the intention of the process according to U.S. 2009/0156841 was to obtain FDCA, the product isolated and erroneously characterized as being FDCA was in fact the starting material acetoxymethyl furfural (AMF). Under the low temperature conditions deployed (100° C.), AMF is quite stable, as was already reported by Partenheimer (see above).
In U.S. 2009/0156841 a 1H NMR spectrum is shown in FIG. 8 and suggested that it is the spectrum of the product that was identified as FDCA. However, this is not the case. The 1H NMR spectrum of the product shown in FIG. 8 is the same as that in FIG. 6 and represents the starting material AMF. The 1H NMR spectrum of FDCA shows a singlet at a shift of about 7.26 ppm. Moreover, the product is described as a tan solid. In the experience of the present inventors, AMF is a tan solid, while FDCA is a white solid. It would seem that no FDCA was obtained in the experiments according to U.S. 2009/0156841.
The experiments executed under the conditions of U.S. 2009/0156841 were repeated. These comparative experiments confirm the low reactivity of AMF under conditions given in U.S. 2009/0156841. Thus, a person skilled in the art would therefore have concluded that FDCA cannot be obtained in interesting yields from AMF using the conditions that are reported in U.S. 2009/0156841, i.e., using a Co/Mn/Br catalyst in acetic acid at between 85 and 110° C. within a time frame of from 100 and 150 minutes. In Example 7 of U.S. 2009/0156841, slightly more than 50% of the starting material was the only product isolated from the reaction.